The goal of health monitoring technologies is to know at any time, for any aircraft in the fleet, the structural integrity of the landing gear, the amount of remaining fatigue life in the landing gear, the landing gear servicing information (such as shock strut pressure and fluid volume, tire pressure and temperature, and brake condition), and the internal status of all on-board electronics and systems related to the landing gear system.
Being able to measure and assess the safety and integrity of the landing gear and landing gear system is of vital interest to the public safety.
The current process for deciding that an airplane has had a “hard landing”, and thus has compromised the safety and integrity of the landing gear, is based on a subjective assessment by the flight crew. Because of the lack of reliable quantitative data, errors are made in this assessment. As a result, an airplane may be grounded unnecessarily, at a considerable cost of time and money, or conversely, a damaged airplane can continue in service, thus compromising public safety.
In addition to this current practice, servicing and maintenance are scheduled to take place at pre-determined intervals. This results in some servicing and inspections taking place before it is required, thus resulting in considerable additional cost of time and money. Conversely, in some cases, the landing gear may be in need of servicing, maintenance or replacement before the next scheduled time. In the interests of the public safety, it is better to be safe than sorry and so maintenance and servicing schedules tend to be very conservative.
Landing gear health monitoring systems involve several unique issues that differentiate it from all other airplane systems and the airframe itself. Airframes are made from relatively ductile aluminum alloys that can withstand relatively long cracks that grow over time. These aluminum structures can sustain fairly significant corrosion before the airplane's fitness for service is compromised. In contrast, landing gears are made from very high strength (but relatively low toughness) steel, aluminum, and titanium alloys with critical defect sizes that are much smaller.
This significant difference is also reflected in the fact that aircraft design and approval methodologies are quite different between the airframe and the landing gear. For example, the airframe uses “damage tolerant” design methodologies, which allow cracks of known sizes to exist in structural members, applied to fatigue dominated zones in the airframe compared to “safe life” design methods, which do not permit cracks, used in the landing gear.
As a result, many of the technologies and articles related to health monitoring of the airframe, e.g. measuring the dynamic characteristics of the structure and then inferring whether certain joints have failed or cracks have grown, are of little interest when considering health monitoring of the landing gear. Similarly, the sensors and technology involved for airplane systems are not sensitive enough to resolve the very small defects of interest or displacements of interest for landing gear applications.
The present invention provides a system and method that utilizes extensive destructive and non-destructive testing and analysis of full-scale landing gear, extensive engineering modeling of the landing gear design and modeling of the causes of failure, and extensive experience with analysis of landing gears in-service. This integrated system and method utilizes an arrangement of sensors and sub-systems and an extensive database of information such as the original manufactured condition of the landing gear, amount and type of maintenance, in-service history of similar landing gear, history of the specific landing gear of interest, prior in-service loads, and number and type of hard landings; and sophisticated analytical techniques in order to determine the safety of the landing gear and/or need for service, maintenance or replacement. The present invention can disseminate and report the need for service, maintenance or replacement to a spectrum of interested parties including: pilots and flight crews, maintenance personnel, airline operators, ground crew and regulatory authorities.